The discovery of a vast number of disease biomarkers and the establishment of miniaturized microfluidic systems have opened up new avenues to devise methods and systems for the prediction, diagnosis and treatment of diseases in a point-of-care setting. Point-of-care testing is particularly desirable because it rapidly delivers results to medical practitioners and enables faster consultation. Early diagnosis allows a practitioner to begin treatment sooner and thus avoiding unattended deterioration of a patient's condition.
In many diagnostic devices that perform immunoassays, dilution of the test sample prior to running the assay is preferable for a variety of reasons. For example, sample dilution can help removal of matrix effects, unbind the target molecules from other binding proteins in the sample, bring the target analyte concentration into the measurable range of the assay, and/or provide sufficient liquid to perform multiple assays (especially when the available sample is small, such as a drop of fluid). In most cases, the dilution must be exquisitely precise or risk compromising the precision of the assay result. Devices such as those constructed by Abaxis (U.S. Pat. No. 5,472,603), Biotrack (U.S. Pat. Nos. 4,946,795 and 5,104,813), and Miles (U.S. Pat. No. 5,162,237) typically perform dilutions with a precision to about 2%; however, such devices may require a large volume of test sample, which is more difficult to obtain in a point-of-care setting.
Often, when measuring a blood sample, analytes in serum or plasma are of interest. One reason is that many analytes are found in the fluid part of blood namely plasma. For numerous blood tests performed for clinical purposes, the final reported concentration typically needs to relate to the concentration of blood serum or blood plasma in a diluted sample. In most cases, blood serum or blood plasma is the test medium of choice in the lab. Two operations may be necessary prior to running an assay, dilution and red blood cell removal. Blood samples vary significantly in the proportion of the sample volume occupied by red cells (the hematocrit which varies from about 20-60%). Furthermore, in a point-of-care environment when assay systems are operated by non-expert personnel, the volume of sample obtained may not be that which is intended. If a change in volume is not recognized, it can lead to error in the reported analyte concentrations.
Thus, there remains a considerable need for point-of-care devices that can provide accurate and rapid data collection, transmission, analysis, and/or real-time medical consultation or decision making. In particular, there remains a need in the art for a point-of-care fluidic device that can measure the concentration of plasma in a sample, and determined the apparent dilution ratio to effect an accurate quantification of an analyte of interest present in a small sample of blood. The present invention satisfies these needs and provides related advantages as well.